1. Field of the Invention
This invention relates to inspecting flaws in semiconductor wafers. More particularly, this invention relates to inspecting defects on the circumference of semiconductor wafers.
2. Description of the Related Technology
Semiconductor wafers used in integrated circuit fabrication processes are generally thin circular semiconductor plates. The semiconductor wafers undergo thermal and physical stresses during various treatments of the fabrication processes. Sometimes, wafers have some internal or surface defects such as cracks and scratches. The portions of the wafers having such defects may produce defective integrated circuits, reducing the yield of the fabrication processes. Also, an existing crack or other defects of a wafer may aggravate by thermal and physical stresses applied thereto during the fabrication processes.
Wafers having such defects may cause more serious problems. For example, if a defective wafer breaks during the processes, the wafer can no longer be used. Also, if multiple wafers are processed simultaneously in the same chamber as is common in an automated fabrication process, pieces of a broken wafer may scratch or harm many other flawless wafers in the same batch. The broken pieces may damage the expensive semiconductor fabrication equipment.
One aspect of the present invention provides an apparatus for inspecting defects of a semiconductor wafer. The wafer is a thin plate comprising two surfaces and a circumference neighboring the two surfaces. The apparatus comprises a wafer holder; a camera configured to capture images of a circumference of a wafer subject to the inspection and to generate data of the captured images; and a processor configured to process the data from the camera so as to identify defects on the circumference of the wafer.
In the apparatus, the camera is configured to continuously capture the images of the circumference. The apparatus further comprises a mechanism configured to effect at least one of linear movement of a camera location and changes of a camera direction. The apparatus further comprises a light source configured to illuminate the circumference of the wafer. The light source comprises a longitudinal light bulb having a longitudinal direction, and the wafer holder is configured to hold the wafer such that the two surfaces of the wafer is substantially parallel to the longitudinal direction of the light bulb. The wafer holder is configured to hold the wafer in a way that the camera captures the images of the circumference of the wafer. Also, the wafer holder is configured to hold a plurality of wafers, which are concurrently subject to the inspection.
The apparatus further comprises a mechanism configured to couple with the holder, wherein the mechanism is configured to move the wafer held in the holder without changing a distance between the camera and a point on the circumference of the wafer, which is the closest from the camera. The apparatus mechanism comprises a lower support table and an upper linear motion table configured to linearly move on the lower support table while being coupled therewith. The upper linear motion table is configured to couple with the wafer holder. The mechanism further comprises an actuator driving the upper linear motion table to linearly move. The mechanism is configured to rotate the wafer held in the holder about an axis substantially perpendicular to the surfaces of the wafer. The wafer holder comprises a flat aligner, which further comprises the mechanism configured to rotate the wafer. The apparatus further comprises a mechanism configured to keep an angle between a central axis of a lens of the camera directing a point on the circumference and a tangent of the point constant during the capturing images. The apparatus further comprises a display configured to display inspection results; an input device configured to input information relating to the wafer subject to the inspection and commands to the apparatus; a memory configured to store image data of circumference of the wafer. The camera comprising a charge coupled device (CCD) line scan camera.
Another aspect of the present invention provides a method of inspecting defects on a circumference of a semiconductor wafer. The method comprises: obtaining images of a circumference of a semiconductor wafer; generating data indicative of the images of the circumference; and processing the data, thereby identifying defects on the circumference of the semiconductor wafer.
In the method, the step of obtaining images comprises capturing images of an entire circumference of the wafer with a camera. Also the step comprises moving at least one of the wafer and the camera. The moving is performed without changing a distance between the camera and a point on the circumference of the wafer, which is the closest from the camera. In case the wafer circumference comprises a round portion and a linear portion, the linear moving is performed during capturing images of the linear portion, and the rotation is performed during capturing images of the round portion.
Also, the moving comprises rotating the wafer about an axis substantially perpendicular to the surfaces of the wafer. The wafer surfaces are substantially circular and the axis is a central axis of the circular surfaces. In capturing images while rotating the wafer, the camera directs the central axis of the circular surfaces. The obtaining images comprise capturing images of circumference of a plurality of wafers. Also, during the capturing images, an angle between a central axis of a lens of the camera directing a point on the circumference and a tangent of the point is kept constant. The method further comprises illuminating the circumference of the wafer during the obtaining of the images. The illuminating comprises illuminating the circumference with a longitudinal light source having a longitudinal direction, in which the longitudinal direction of the light source is substantially parallel to the surfaces of the wafer.
Further, the present invention provides a method of fabricating integrated circuits on a semiconductor wafer. This method comprises inspecting defects on a circumference of a semiconductor wafer, and thereafter subjecting the semiconductor wafer to at least one of chemical and thermal treatments, thereby fabricating integrated circuits. The inspection comprises: capturing images of a circumference of a semiconductor wafer; generating data indicative of the images of the circumference; and processing the data, thereby identifying defects on the circumference of the semiconductor wafer. The inspection stage may also have all the features of the method of inspecting defects as summarized above.